A variety of entities, such as, but not limited to government/military agencies, hospitals, manufacturers, and financial institutions, customarily issue various types of substrates (e.g., documents) that incorporate one or more inspectable security features (such as microprints, watermarks, threads, and the like), that serve to provide evidence of authenticity and/or tampering/counterfeiting, and thereby enable a recipient to determine whether the substrate is valid for its intended purpose.
Unfortunately, the continuously expanding degree of sophistication of tampering and counterfeiting threats to such security measures has not only resulted in a substantial increase in the complexity and cost of such visual security features, but has reached a point of diminishing returns in which the degree of security is degraded. For non-limiting examples of previously proposed document security measures, attention may be directed to the following U.S. Pat. Nos.: 4,661,983; 5,549,953; 4,662,653; 5,218,472; 5,456,498; 5,291,205; and 5,204,681.